在每个循环迭代中创建对象

Question

我正在使用内置的 z80 导航控件，这里是用于演示的 link： Z80 Navigation Menu

如果有人看到该控件，它有一个对象来创建菜单，如父菜单和在它下面的子菜单。类似于以下内容：

public List<NavBarItem> sampleDynamicNav; //List of navbar objects
public DemoItems()
{
    //Create object instance here and assign the parent as well child menus here
    sampleDynamicNav = new List<NavBarItem> {
    new NavBarItem {ID = 1, Text = "UserInfo", Icon = new ItemIcon {Default = SampleProject.Properties.Resources.nav_new_home, Hover = SampleProject.Properties.Resources.nav_new_home, Selected = SampleProject.Properties.Resources.nav_new_home}, ToolTip = "tooltip Main Menu", Height = 40,
        Icon = new ItemIcon {Default = SampleProject.Properties.Resources.nav_new_home, Hover = SampleProject.Properties.Resources.nav_new_home, Selected = SampleProject.Properties.Resources.nav_new_home }, ToolTip = "tooltip Desktop"},
        Childs = new List<NavBarItem> {
                    new NavBarItem {ID = 41, Text = "Add/Edit Users", Height = 30 },
                    new NavBarItem {ID = 42, ParentID = 1, Text = "Inactive User", Height = 30}
    };
}

如果我们静态分配菜单，这就非常简单了。但我坚持了下来，当尝试动态添加它们时，我的意思是从数据库创建菜单，如下所示：

public DemoItems()
{
    foreach (var parent in GetParent("USER-0001"))
    {
          foreach (var child in GetChild(parent.MenuNo))
          {
            sampleDynamicNav = new List<NavBarItem> {
                 new NavBarItem {
                 ID = parent.MenuNo, Text = parent.MenuName, Icon = new ItemIcon {Default =  SampleProject.Properties.Resources.nav_new_home, Hover = SampleProject.Properties.Resources.nav_new_home, Selected = SampleProject.Properties.Resources.nav_new_home}, ToolTip = "tooltip Main Menu", Height = 40,
                 Childs = new List<NavBarItem> {
                                    new NavBarItem {ID = child.MenuNo, ParentID = parent.MenuNo, Text = child.MenuName, Height = 30 },
                           }
                     }
               };
          }
     }
}

通过上面的代码，应该至少在导航栏中获取父菜单。暂且不说子菜单，在导航栏中显示一个父菜单如下：

但它应该像下面这样，因为有两个父菜单并使用 foreach 循环迭代列表（GetParents() returns 对象列表）：

我不知道我是否需要为此做任何其他事情，想知道我是否可以循环浏览导航栏的子属性，如下所示：

foreach (var child in GetChild(parent.MenuNo))
{
   Childs = new List<NavBarItem> {
            new NavBarItem {ID = child.MenuNo, ParentID = parent.MenuNo, Text = child.MenuName, Height = 30 },
}

N.B：当尝试用循环迭代子属性时，它现在会抛出错误。第二个内部循环工作并取出子菜单但是说，父菜单有两个子菜单，它 returns 1 当时。我调试了列表，它 returns 像往常一样有两个父菜单，但没有显示在导航栏中。

GetParents 方法:

/**Get Menu Details - Starts**/
public IEnumerable<UserViewModel> GetParent(string empNo)
{
       List<UserViewModel> lstUser = new List<UserViewModel>();

       string query = "SELECT DISTINCT M.PARENT, M.MENUNO, M.MENUNAME FROM (SELECT DISTINCT M.MENUNO, M.MENUNAME, M.PARENT " +
                      "FROM USER_DETAILS U INNER JOIN USER_GROUP_DETAILS UG ON UG.EMPNO = U.EMPNO " +
                      "INNER JOIN ASSIGN_MENU_DETAILS AM ON AM.GROUPNO = UG.GROUPNO INNER JOIN MENU_DETAILS M " +
                      "ON M.MENUNO = AM.MENUNO WHERE U.EMPNO = '" + empNo + "' " +
                      "UNION ALL " +
                      "SELECT DISTINCT M.MENUNO, M.MENUNAME, " +
                      "M.PARENT FROM MENU_DETAILS M " +
                      "INNER JOIN MENU_DETAILS C " +
                      "ON C.PARENT = M.MENUNO) m WHERE M.PARENT = '0' ORDER BY M.PARENT";

        DataTable dt = SelectData(query);

        if (dt != null && dt.Rows.Count > 0)
        {
            foreach (DataRow dr in dt.Rows)
            {
                UserViewModel bo = new UserViewModel();
                bo.Parent = Convert.ToInt32(dr["PARENT"].ToString());
                bo.MenuNo = Convert.ToInt32(dr["MENUNO"].ToString());
                bo.MenuName = dr["MENUNAME"].ToString();

                lstUser.Add(bo);
            }
        }
   return lstUser;
}
/**Get Menu Details - Ends**/

Answer 1

您可以创建以下辅助方法并使用它们创建一个 List<NavBarItem 接受任何类型的数据源作为输入，包括 DataTable、List<YourEntity> 或任何其他 IEnumerable<T>.

因此，无论您拥有何种数据存储，都可以使用以下方法。

它依赖于递归算法来创建树。要从任何类型的数据源创建树，您需要了解以下信息：

数据来源
如何检测数据源中的项目是否为根项目
如何在数据源中查找项目的子项目
如何从数据源项创建树项。

以下方法通过询问以上信息创建 NavBarItem 层次结构的列表：

private IEnumerable<NavBarItem> GetNavBarItems<T>(
    IEnumerable<T> source,
    Func<T, Boolean> isRoot,
    Func<T, IEnumerable<T>, IEnumerable<T>> getChilds,
    Func<T, NavBarItem> getItem)
{
    IEnumerable<T> roots = source.Where(x => isRoot(x));
    foreach (T root in roots)
        yield return ConvertEntityToNavBarItem(root, source, getChilds, getItem); ;
}

private NavBarItem ConvertEntityToNavBarItem<T>(
    T entity,
    IEnumerable<T> source,
    Func<T, IEnumerable<T>, IEnumerable<T>> getChilds,
    Func<T, NavBarItem> getItem)
{
    NavBarItem node = getItem(entity);
    var childs = getChilds(entity, source);
    foreach (T child in childs)
        node.Childs.Add(ConvertEntityToNavBarItem(child, source, getChilds, getItem));
    return node;
}

例子

我假设您已将数据加载到以下结构中：

var dt = new DataTable();
dt.Columns.Add("Id", typeof(int));
dt.Columns.Add("Name", typeof(string));
dt.Columns.Add("ParentId", typeof(int));

dt.Rows.Add(1, "Menu 1", DBNull.Value);
dt.Rows.Add(11, "Menu 1-1", 1);
dt.Rows.Add(111, "Menu 1-1-1", 11);
dt.Rows.Add(112, "Menu 1-1-2", 11);
dt.Rows.Add(12, "Menu 1-2", 1);
dt.Rows.Add(121, "Menu 1-2-1", 12);
dt.Rows.Add(122, "Menu 1-2-2", 12);
dt.Rows.Add(123, "Menu 1-2-3", 12);
dt.Rows.Add(124, "Menu 1-2-4", 12);
dt.Rows.Add(2, "Menu 2", DBNull.Value);
dt.Rows.Add(21, "Menu 2-1", 2);
dt.Rows.Add(211, "Menu 2-1-1", 21);

然后把它转换成List<NavBarItem>，可以用下面的代码：

var source = dt.AsEnumerable();
var list = GetNavBarItems(
        source,
        (r) => r.Field<int?>("ParentId") == null,
        (r, s) => s.Where(x => x.Field<int?>("ParentId") == r.Field<int?>("Id")),
        (r) => new NavBarItem()
        {
            ID = r.Field<int>("Id"),
            Text = r.Field<string>("Name"),
            ParentID = r.Field<int?>("ParentId")
        }).ToList();

因此，您将具有以下结构：

Menu 1
   Menu 1-1
       Menu 1-1-1
       Menu 1-1-2
   Menu 1-2
       Menu 1-2-1
       Menu 1-2-2
       Menu 1-2-3
       Menu 1-2-4
Menu 2
    Menu 2-1
        Menu 2-1-1

备注

不想安装包，但想测试结构的可以使用下面的NavBarItem class:

public class NavBarItem
{
    public NavBarItem()
    {
        Childs = new List<NavBarItem>();
    }
    public int ID { get; set; }
    public int? ParentID { get; set; }
    public string Text { get; set; }
    public List<NavBarItem> Childs { get; set; }
    public override string ToString()
    {
        return Text;
    }
}

Answer 2

我用你的代码示例 @Reza Aghaei 尝试了以下操作，并使用 TreeView 控件卡住了一点，如下所示：（它有效但出现错误，下面一行）

private void frmSampleApp_Load(object sender, EventArgs e)
{
    var dt = new DataTable();
    dt.Columns.Add("Id", typeof(int));
    dt.Columns.Add("Name", typeof(string));
    dt.Columns.Add("ParentId", typeof(int));

    dt.Rows.Add(1, "Menu 1", DBNull.Value);
    dt.Rows.Add(11, "Menu 1-1", 1);
    dt.Rows.Add(111, "Menu 1-1-1", 11);
    dt.Rows.Add(112, "Menu 1-1-2", 11);
    dt.Rows.Add(12, "Menu 1-2", 1);
    dt.Rows.Add(121, "Menu 1-2-1", 12);
    dt.Rows.Add(122, "Menu 1-2-2", 12);
    dt.Rows.Add(123, "Menu 1-2-3", 12);
    dt.Rows.Add(124, "Menu 1-2-4", 12);
    dt.Rows.Add(2, "Menu 2", DBNull.Value);
    dt.Rows.Add(21, "Menu 2-1", 2);
    dt.Rows.Add(211, "Menu 2-1-1", 21);

    var source = dt.AsEnumerable();
    var list = GetNavBarItems(
            source,
            (r) => r.Field<int?>("ParentId") == null,
            (r, s) => s.Where(x => x.Field<int?>("ParentId") == r.Field<int?>("Id")),
            (r) => new NavBarItem()
            {
                ID = r.Field<int>("Id"),
                Text = r.Field<string>("Name"),
                ParentID = r.Field<int?>("ParentId")
            }).ToList();

    foreach (var item in list)
    {
        TreeNode parentNode = null;
        parentNode = treeView1.Nodes.Add(item.Text.ToString());

        BindData(Convert.ToInt32(item.ParentID), parentNode);
    }
}

public void BindData(int parentId, TreeNode parentNode)
{
    var dt = new DataTable();
    dt.Columns.Add("Id", typeof(int));
    dt.Columns.Add("Name", typeof(string));
    dt.Columns.Add("ParentId", typeof(int));

    dt.Rows.Add(1, "Menu 1", DBNull.Value);
    dt.Rows.Add(11, "Menu 1-1", 1);
    dt.Rows.Add(111, "Menu 1-1-1", 11);
    dt.Rows.Add(112, "Menu 1-1-2", 11);
    dt.Rows.Add(12, "Menu 1-2", 1);
    dt.Rows.Add(121, "Menu 1-2-1", 12);
    dt.Rows.Add(122, "Menu 1-2-2", 12);
    dt.Rows.Add(123, "Menu 1-2-3", 12);
    dt.Rows.Add(124, "Menu 1-2-4", 12);
    dt.Rows.Add(2, "Menu 2", DBNull.Value);
    dt.Rows.Add(21, "Menu 2-1", 2);
    dt.Rows.Add(211, "Menu 2-1-1", 21);

    var source = dt.AsEnumerable();
    var list = GetNavBarItems(
            source,
            (r) => r.Field<int?>("ParentId") == null,
            (r, s) => s.Where(x => x.Field<int?>("ParentId") == r.Field<int?>("Id")),
            (r) => new NavBarItem()
            {
                ID = r.Field<int>("Id"),
                Text = r.Field<string>("Name"),
                ParentID = r.Field<int?>("ParentId")
            }).ToList();
        TreeNode childNode; 

    foreach (var item in list)
    {
        if (parentNode == null)

            childNode = treeView1.Nodes.Add(item.Text.ToString());

        else

            childNode = parentNode.Nodes.Add(item.Text.ToString());
        BindData(Convert.ToInt32(item.ID.ToString()), childNode); //An unhandled exception of type 'System.WhosebugException' occurred in System.Windows.Forms.dll
    }
}

private IEnumerable<NavBarItem> GetNavBarItems<T>(
IEnumerable<T> source,
Func<T, Boolean> isRoot,
Func<T, IEnumerable<T>, IEnumerable<T>> getChilds,
Func<T, NavBarItem> getItem)
    {
        IEnumerable<T> roots = source.Where(x => isRoot(x));
        foreach (T root in roots)
            yield return ConvertEntityToNavBarItem(root, source, getChilds, getItem); ;
    }

    private NavBarItem ConvertEntityToNavBarItem<T>(
    T entity,
    IEnumerable<T> source,
    Func<T, IEnumerable<T>, IEnumerable<T>> getChilds,
    Func<T, NavBarItem> getItem)
    {
        NavBarItem node = getItem(entity);
        var childs = getChilds(entity, source);
        foreach (T child in childs)
            node.Childs.Add(ConvertEntityToNavBarItem(child, source, getChilds, getItem));
        return node;
    }
}

public class NavBarItem
{
    public NavBarItem()
    {
        Childs = new List<NavBarItem>();
    }
    public int ID { get; set; }
    public int? ParentID { get; set; }
    public string Text { get; set; }
    public List<NavBarItem> Childs { get; set; }
    public override string ToString()
    {
        return Text;
    }
}

N.B：没关系。我知道，这里一团糟，只是为了学习目的而试图弄清楚 - 谢谢。

在每个循环迭代中创建对象

Create Object in Every Loop Iteration

.net

c#

menu

tree-structure

winforms